The present invention relates to a valve control system for electromagnetically actuating intake and exhaust valves of an internal combustion engine.
FIG. 2 of the accompanying drawings shows a conventional internal combustion engine. When fuel is combusted in a combustion chamber 1. a piston 2 is lowered to rotate a crankshaft 4 through a connecting rod 3. Intake and exhaust valves 8, 9 disposed in a cylinder head are opened and closed by rocker arms 6, 7 operated by a camshaft 5 which is operatively coupled to the crankshaft 4 by a timing belt and pulleys.
When the internal combustion engine operates in a high-speed range, periods of time required to introduce intake air and discharge exhaust gases are reduced, and hence intake air has to be introduced and exhaust gases have to be discharged quickly. If the area in which the intake and exhaust valves are open is small, then the amounts of intake air introduced and exhaust gases discharged are lowered, resulting in a reduction in volumetric efficiency of intake air. It is desirable that the area in which the intake and exhaust valves are open with respect to the crankshaft angle be smaller when the engine rotational speed is lower and larger when the engine rotational speed is higher.
However, since the intake and exhaust valves are opened and closed by cams on the camshaft 5 that rotates in synchronism with the crankshaft 4, as described above, the valve opening area is determined solely by the profile of the cams. It is impossible to vary the valve opening area depending on the engine rotational speed.
Valve control systems in which intake and exhaust valves are operated by electromagnetic actuator means have been proposed as disclosed in Japanese Laid-Open Patent Publications Nos. 58-183805 and 61-76713. These publications only disclose that the intake and exhaust valves are ogerated by the electromagnetic actuator means.